Metal-ceramic composite structures have been utilized for both sensing and actuation applications. In U.S. Pat. Nos. 4,999,819 and 5,276,657 to Newnham et al., a central piezoelectric wafer has metal end caps adhered to the peripheries of either surface of the piezoelectric wafer. The piezoelectric wafer is poled across its thickness dimension so that application of a voltage thereacross results in a radially directed movement of the wafer's circumference and a concurrent flexure of the attached end caps. Further, application of a force to the end caps causes a voltage to be induced across the piezoelectric wafer.
In an actuator embodiment, application of a voltage across the piezoelectric wafer causes a radially directed inward movement of the circumference of the wafer, thereby causing a distortion of the end caps and a resultant movement of an actuation surface thereof. In a sensor embodiment, application of a pressure to the end caps is translated through the joinder thereof to the wafer into a physical distortion of the wafer which, in turn, induces an output voltage proportional to the applied pressure. In both of the embodiments, the end caps either (i) respond to a lateral movement of the piezoelectric wafer by moving in a direction orthogonal to the surface of the wafer (actuator) or (ii) respond to an applied pressure in the orthogonal direction by stressing the wafer (sensor). Neither device has the capability of producing movements in the rotary direction or responding thereto.
The prior art includes teachings relating to the structure and operation of ultrasonic motors. U.S. Pat. No. 5,254,899 to Suzuki et al. discloses an ultrasonic motor which employs traveling wave bending modes that are excited on a ring-type unimorph piezoelectric element. Conventional ultrasonic motor designs evidence complex structures. Further, the traveling wave type ultrasonic motor requires plural power supplies, one for a sine voltage and one for a cosine voltage.
U.S. Pat. No. 5,296,776 to Wind et al. describes timepiece motor which utilizes a piezoelectrically driven rotor to incrementally rotate within a fixed stator arrangement.
It is an object of this invention to provide an improved ultrasonic motor which evidence's a simple and inexpensive design.
It is another object of his invention to provide an improved ultrasonic motor which is capable of providing both rotary and linear motions.